1. Field of Invention
The invention relates to an improved corrugator roll for forming a web of corrugated paperboard and, more particularly, to an improved corrugator roll having a portion of the roll surface selectively hardened to a predetermined depth. A corrugator roll hardened in accordance with the teachings of the present invention demonstrated superior wear qualities while not being susceptible to cracking and chipping.
2. Description of the Prior Art
Corrugating rolls are used in machinery such as single-facer corrugators which are used in the manufacture of corrugated paperboard. A detailed description of a typical single-facer is given in Moser et al., U.S. Pat. No. 3,390,040. Since the typical single-facer machine is fully described therein, its structure and operation will not be further described herein, except where necessary to explain the present invention.
A typical corrugating roll in use today is 87 inches long, 12 inches in diameter and weighs approximately 2100 pounds. Certain prior art rolls are forged from alloyed steel and machined to the proper configuration. To use ordinary machining techniques, hardness of the base metal of the corrugator roll is limited to approximately 40 R.sub.c. Certain other prior art rolls are rough machined using ordinary cutting tools and are then hardened by conventional heat treatment. The heat treatment distorts the machined roll, necessitating the use of grinders and the like to regain the desired dimensions. The additional grinding operation requires an additional expense in plant equipment and also involves an expense for the additional labor. These increased operations necessarily increase the cost of a hardened roll. In both types of prior art rolls the entire base metal of the roll is of uniform hardness.
In order to extend roll life, the entire surface of both types of rolls are generally chrome plated or coated with metallic oxide. While chrome plating and oxide coating do in fact extend the operational life of the roll, there are problems with their use. Metallic oxide coatings are expensive and it is difficult to get a good finish on this type of coating. Both chrome plated and oxide coated rolls are susceptible to cracking and chipping. Once they have cracked or chipped, the wear caused by the sliding of the paper web over the roll greatly increases. Since the cracking or chipping usually occurs at the flute tip, the point of maximum sliding friction, the flute tips wear much faster than the rest of the roll causing a loss of caliper. When the caliper of the roll is lost, the roll must either be replaced or reground.
The present invention overcomes the foregoing problems of the prior art by providing an improved corrugator roll which has superior wear characteristics while being economical to both manufacture and use.